Sorry to resurrect this thread. But, I was searching for "Miracast" and came across this one.
Yesterday, I was using my SP2 in a meeting with the PTV3000. I was displaying a slide deck which included HD videos. The meeting lasted two hours. Before the meeting the SP2 was unplugged too - so a total of about 3 hours of use - solely on battery from an initial full charge.
Battery setting was on High Performance (standard settings), WiFi was turned on (obviously) as was Bluetooth and a USB 3.0 receiver for a advancing slides via a remote. Regrettably, the SP2 gave a battery warning about 30 seconds before powering down. I wish I could have gotten 3 hours out of it. It was rather embarrassing, but wasn't the end of the world.
I think the issue is with my specific SP2. I just don't think I get the yield that most users get. Going to search for the command to issue battery results and I wonder if mine is just a wimpy one.